1. Technical Field
The present invention relates to an image forming apparatus such as a printer, a copying machine, or a facsimile.
2. Related Art
A related art example of an image forming apparatus with an electrophotographic process, such as a printer, copying machine, or facsimile, is disclosed in JP-A-2003-54097. This type of image forming apparatus generally uses two or more kinds of power supply voltages as power sources for driving an internal circuit. For example, components containing a microprocessor or the like, such as a controller for controlling the entire operation of the image forming apparatus, and a logic circuit that executes image signal processing and other functions, need a low-voltage (for example, 5 V) power source, while mechanisms such as a motor for driving a photosensitive drum and a paper-feed mechanism, and a laser unit as a light source for light exposure, that require high electric power need a high-voltage (for example, 24 V) power source.
In a general image forming apparatus, a switch that opens or closes a circuit in conjunction with the opening or closing action of a cover for covering the internal content of the main body is provided on the circuit in order to cut off power supply to a motor and other components when the cover is opened in the case where a malfunction (such as paper jamming) has occurred. However, when the switch opens the circuit, cutting off the power, and then closes the circuit again, a high inrush current sometimes flows into a condenser (capacitative load) mounted on a motor control substrate or similar, which is the power supply destination. The upper limit is set for a current value at which current can be passed through the switch, and the inrush current sometimes exceeds that upper limit. With that kind of malfunction problem, a step to avoid a high inrush current flowing into the switch is taken by providing, in addition to the above-mentioned switch, electronic switches such as field-effect transistors (FET) on a power supply path in order to divide the power supply destination, and turning on the respective transistors sequentially at certain time intervals. Moreover, after the cover has been opened and then closed in order to, for example, mount an optional device, in other words, after the switch and the FETS have been opened to cut off power, and then closed again, and if a short-circuit occurs due to, for example, inappropriate mounting of the optional device, an abnormal current may still flow into the optional device.
However, the image forming apparatus disclosed in JP-A-2003-54097 has the problem of incapability to appropriately control a power supply voltage in a component connected to the FETs if an abnormal current is generated in the power supply path due to a short circuit or similar.